Il] VENATION, TEXTURE, APEX 21 



Further characters of the leaves are derived from their 

 texture, apex, margins, mid-ribs and venation, hairiness, and 

 especially the presence and characters of the longitudinal 

 ridges which run aloug the upper or lower surface in many 

 cases. 



The venation is parallel from base to apex in nearly 

 all our grasses, but such is not always the case — e.g. in 

 the exotic Panicum plicatum the mid-rib, which enters the 

 leaf with several vascular bundles, gives off strong and 

 weak veins below, which first diverge and then run in arches 

 which converge upwards : this leaf is also remarkable in 

 being plaited (plicate) in vernation. In Arundo Donax 

 also the veins, though approximately parallel, do not all 

 run to the apex of the tapering leaf; the outer ones end 

 above in the margins and are shorter than the mid-rib. 



As regards texture, the leaves of most grasses are thin 

 and herbaceous ; but in some they are dry and harsh to 

 the touch. They are thin and dry in Agropyrum cani- 

 num, Hordeum pratense, H. murinum, Avena pratensis, &c., 

 very hard and leathery (coriaceous) in Psamma, Nardus, 

 species of Festuca, Aira, Agropyrum junceum, Elymus, &c. 

 In aquatic grasses like Glyceria, the leaf is almost spongy 

 owing to the large air-chambers developed in the tissues. 

 These are easily visible with a lens. 



The apex is in most cases slender and tapering — 

 acuminate; but in some it is merely brought to a point 

 (acute) as in Catabrosa, Glyceria and several species of 

 Poa and Avena, &c., usually flat, but somewhat hooded or 

 curved up in some Poas. In cases where the leaves are 

 setaceous or subulate, the apex is like a thin tapering 



